Papers by Author: Catherine Joulian

Abstract: In bioleaching processes using autotrophic bacteria, CO₂ is the carbon source for the growth of the microorganisms and its availability is dependent on gas mass transfer. The objective of this study was to investigate the demand in CO₂ in complex copper concentrate bioleaching operations and to optimize CO₂ supply. Batch tests in 2L-stirred reactors at 10%_w/v solid load were performed to study the need for CO₂-supplementation and to determine the adequate CO₂ partial pressure in the gas inlet. The results show that Fe oxidation (and thus microbial activity) is delayed when air is injected without CO₂-supplementation. CO₂-supplementation improves leaching kinetics since Cu dissolution rate increases from 84 mg/L/h with air solely to 120 mg/L/h when CO₂ is added to air. The study proposes also a methodology to determine G/L transfer components and to asses CO₂ limitations in the system. It shows that the microorganisms are not only sensitive to the transfer rate of CO₂ from the gas to the liquid phase, but also to the availability of CO₂ in solution.

Abstract: Kupferschiefer-type ore represents an important source for base metals and several studies concerning the bioleaching of black shale ores and Cu concentrates have been carried out with focus on various microbial communities and processing parameters. However, the incomplete dissolution of chalcopyrite remains a key issue for copper ore bioleaching improvement and requires further investigations in order to ensure an optimal control of the process for upscaling. Our study clearly showed that bioleaching tests are characterized by two separate phases with a distinct optimal temperature. A distinct effect of the temperature on the copper recovery and the advantage of temperature ramp in order to enhance copper bioleaching and chalcopyrite dissolution were demonstrated.

Abstract: In bioleaching processes, gas transfer is often considered as one of the key mechanisms that will influence the leaching efficiency and more precisely the leaching rate. Oxygen can be a limiting factor in bacterial leaching because of its low solubility. One way to overcome this phenomenon consists in increasing the oxygen partial pressure in the gas stream supplied to the leach pulp. The primary objective of this work was to investigate the use of oxygen-enriched gas in bioleaching stirred reactors and its impact on the consortium dynamics. First tests were performed at lab scale in four successive series of 2-L bioreactors alimented either with air or with oxygen enriched gas. The microbial consortium used has proven its efficiency on several ores such as cobaltiferous pyrite and polymetallic ores in former research projects (BioMine, BioShale, ProMine). The community diversity was remarkably reproducible irrespective of the type of gas supply, in each of the successive series of reactors. Only minor changes occurred after subculturing from one batch series to the next one, highlighting the high stability of the established consortium. Different oxygen partial pressures (from 20% to 50%) were then tested in a 20-L continuous reactors pilot experiment. There was no impact on the community diversity, showing the high tolerance to oxygen of the bioleaching strains and their capacity to easily survive 50% oxygen input. The bioleaching efficiency in terms of rate and metal leaching did not seem to be changed. The use of enriched oxygen gas is not detrimental to the bioleaching strains and may be used in order to improve process operation (gas transfer, heat management...).

Abstract: A process for the precipitation of trivalent arsenic sulphide in sulphate-reducing condition at low pH would be very attractive due to the high arsenic content (60%) in the final precipitate. A bacterial consortium able to reduce sulphate at pH 4.5 served to inoculate column bioreactors that were continuously fed with As(V) or As(III), glycerol and/or hydrogen, at pH values between 2 and 5. The diversity, functionality and evolution of the consortium colonizing the bioreactors were characterized by means of biomolecular tools, in relation with operating parameters (pH, As, sulphide, acetate). The highest As removal rate obtained during these experiments was close to 3 mg.l-1.h-1 using As(V) as the initial arsenic form, while precipitation rates were improved using As(III). When glycerol was replaced by hydrogen in a bioreactor containing a mature biofilm, sulphate-reducing activity increased roughly. Organisms related to Desulfosporosinus were the only sulphate-reducing bacterium (SRB) detected in the bioreactor. arrA genes, involved in As(V) dissimilatory reduction, were also detected and suggested that As(V) was reduced by a Desulfosporosinus-like organism. Molecular fingerprints evidenced an evolution of the bacterial population structure according to changes in operating conditions.

Abstract: Catalyzed reporter deposition fluorescence in situ hybridization (CARD-FISH) is a powerful method with a growing number of applications in the quantitative evaluation of microbial populations of complex ecosystems. CARD-FISH is an improvement over traditional fluorescence in situ hybridization (FISH) especially suitable for aquatic habitats with small, slow growing, or starving bacteria, in which the signal intensities of hybridized cells is frequently below detection limits or lost in high fluorescence background of dense mineral matrixes. In this work we report the development of protocols and probes for the identification and quantification of the microorganisms involved in the continuous bioleaching of a cobaltiferrous concentrate using a four tank-leaching reactor operated by BRGM. After steady state was reached, samples were taken to identify and quantify the microorganisms present in the each of the tanks used in the process.

Abstract: Black schist ores in Finland are often enriched with sulfide minerals, containing a variety of base metals such as nickel, copper, zinc and cobalt. As these ores are low grade with respect to the metals contained and the sulfide minerals cannot be effectively concentrated from the schists, they are currently being studied with regard to their suitability for bioleaching [1]. As part of this investigation, a large-scale column measuring 3 x 3 x 9 m was built and filled with 110 tons of the crushed black schist ore. A solution was circulated in the column for 95 weeks; this solution was adjusted to 1.8 prior to entry in the column and averaged 2.7 when leaving the column. During this time, approximately 22% of Mn, 10% of Ni and 5% of Zn were leached from the ore. Iron was also leached, but precipitated in the column. Any soluble iron in the effluent was mainly Fe (II). During this same time period, total cell counts averaged 3.6 x 107 cells/ml of effluent. On three different occasions over nearly a one-year period, culturable cells were enumerated on a variety of solid media [2] and represented only about 1% of the total cell counts. Of the culturable cells, ironoxidizing acidophiles (namely Acidithiobacillus ferrooxidans) far outnumbered any other acidophile by at least a factor of ten. Changes in populations were also monitored by molecular means (T-RFLP and SSCP) on five different occasions during the same year; again, populations in early samples were dominated by Acidithiobacillus ferrooxidans (at least two strains/sub-species). As the temperature of the column was increased from ~20 to 35°C by heating both the recirculated liquor and the air used for column aeration, the relative abundance of At. ferrooxidans-like bacteria decreased while the abundance of unidentified bacteria increased. Some of these bacteria have also been detected in lab-scale column experiments using the same ore [3]. Total cell counts varied little as the temperature increased, nor was there any change in the rate of metal leaching. It was apparent that even though the leaching of metals from black schist ores was not greatly influenced by increases of temperature in the column, active microbial populations were present and were influenced by temperature.

Abstract: In the frame of a European project (BioMinE - FP6), a continuous bioleaching operation was carried out in a laboratory-scale unit using a cobaltiferous pyrite. The objective of the work was to use this system to investigate mechanisms of microbial activity and mineral oxidation in continuous stirred bioreactors (1x50L - 3x20L). A combination of scientific and technical approaches (molecular ecology, biochemistry and microscopy) was used and various key operating parameters were tested (temperature, nitrogen source, CO2 availability, designed consortia). An increase of temperature of 10°C (35°C to 45°C) had no major influence on the bioleaching efficiency. When the ammonium source was limiting, there was a negative influence on both bacterial growth and bioleaching efficiency. This result was related to a combination of factors such as less bacterial attachment to the pyrite surface and less precipitate formation. CO2 limitation had a very significant negative effect on the bacterial productivity and consequently on the bioleaching efficiency. Nevertheless, the population composition remained unchanged. An important decrease of EPS (sugar) production was also observed. The bacterial strains, that dominate the culture, originated from the deposit in Uganda. It seems that their bioleaching ability was improved over the time when cultured in continuous mode. The culture composition was very stable. The iron-oxidizer L. ferriphilum was the dominant organism in standard (not limiting) conditions, and was always very well represented during the first 3-4 days of residence time. Sulfobacillus sp. BRGM2 also played an important role in the process. This study gives new insights for the application of this technology, and more specifically on the influence of key operating parameters on bioleaching performances, population dynamics and attachment of bacteria to the solid surfaces.